--  Environment definition for synthesis.
--  Copyright (C) 2017 Tristan Gingold
--
--  This file is part of GHDL.
--
--  This program is free software; you can redistribute it and/or modify
--  it under the terms of the GNU General Public License as published by
--  the Free Software Foundation; either version 2 of the License, or
--  (at your option) any later version.
--
--  This program is distributed in the hope that it will be useful,
--  but WITHOUT ANY WARRANTY; without even the implied warranty of
--  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
--  GNU General Public License for more details.
--
--  You should have received a copy of the GNU General Public License
--  along with this program; if not, write to the Free Software
--  Foundation, Inc., 51 Franklin Street - Fifth Floor, Boston,
--  MA 02110-1301, USA.

with Types; use Types;
with Tables;
with Netlists; use Netlists;
with Netlists.Builders;
with Synth.Source;

package Synth.Environment is
   --  A simple signal/variable is either a bit or a std_ulogic
   --  signal/variable, or a bus (bit_vector, std_ulogic_vector, signed,
   --  unsigned...).
   --
   --  Complex signals/variables (records, arrays) are decomposed to simple
   --  signals/variables.
   --
   --  Each simple signal/variable is represented by a Wire_Id.  Synthesis
   --  deals only with these wires or group of them.
   type Wire_Id is private;
   No_Wire_Id : constant Wire_Id;

   function Is_Lt (L, R : Wire_Id) return Boolean;

   --  A Wire is either a signal, a variable or a port.  We need to know the
   --  nature of a wire as the assignment semantic is not the same (a variable
   --  assignment overwrite the old value, while a signal assignment is
   --  effective at the next cycle).
   type Wire_Kind is
     (
      Wire_None,
      Wire_Signal, Wire_Variable,
      Wire_Input, Wire_Output, Wire_Inout
     );

   type Seq_Assign is private;
   No_Seq_Assign : constant Seq_Assign;

   type Conc_Assign is private;
   No_Conc_Assign : constant Conc_Assign;

   function Alloc_Wire (Kind : Wire_Kind; Obj : Source.Syn_Src)
                       return Wire_Id;

   --  Set the gate for a wire.
   --  The gate represent the current value.  It is usually an Id_Signal.
   procedure Set_Wire_Gate (Wid : Wire_Id; Gate : Net);

   --  The current value of WID.  For variables, this is the last assigned
   --  value.  For signals, this is the initial value.
   function Get_Current_Value (Wid : Wire_Id) return Net;

   --  The last assigned value to WID.
   function Get_Last_Assigned_Value (Wid : Wire_Id) return Net;

   --  Read and write the mark flag.
   function Get_Wire_Mark (Wid : Wire_Id) return Boolean;
   procedure Set_Wire_Mark (Wid : Wire_Id; Mark : Boolean := True);

   type Phi_Id is private;
   No_Phi_Id : constant Phi_Id;

   function Get_Wire_Id (W : Seq_Assign) return Wire_Id;
   function Get_Assign_Chain (Asgn : Seq_Assign) return Seq_Assign;
   function Get_Assign_Value (Asgn : Seq_Assign) return Net;

   type Phi_Type is private;

   --  Create a new phi context.
   procedure Push_Phi;

   procedure Pop_Phi (Phi : out Phi_Type);

   --  Destroy the current phi context and merge it.  Can apply only for the
   --  first non-top level phi context.
   procedure Pop_And_Merge_Phi (Ctxt : Builders.Context_Acc;
                                Stmt : Source.Syn_Src);

   --  Handle if statement.  According to SEL, the value of the wires are
   --  those from T or from F.
   procedure Merge_Phis (Ctxt : Builders.Context_Acc;
                         Sel : Net;
                         T, F : Phi_Type);

   --  Sort all seq assign of P by wire id.  Used to more easily merge them.
   function Sort_Phi (P : Phi_Type) return Seq_Assign;

   --  In the current phi context, assign VAL to DEST.
   procedure Phi_Assign (Dest : Wire_Id; Val : Net);

   --  Get current phi context.
   function Current_Phi return Phi_Id;
   pragma Inline (Current_Phi);

   procedure Add_Conc_Assign (Wid : Wire_Id; Val : Net; Stmt : Source.Syn_Src);
   procedure Add_Conc_Assign_Comb
     (Wid : Wire_Id; Val : Net; Stmt : Source.Syn_Src);

   procedure Finalize_Assignments (Ctxt : Builders.Context_Acc);
private
   type Wire_Id is new Uns32;
   No_Wire_Id : constant Wire_Id := 0;

   function Is_Lt (L, R : Wire_Id) return Boolean renames "<";

   type Seq_Assign is new Uns32;
   No_Seq_Assign : constant Seq_Assign := 0;

   type Conc_Assign is new Uns32;
   No_Conc_Assign : constant Conc_Assign := 0;

   type Phi_Id is new Uns32;
   No_Phi_Id : constant Phi_Id := 0;

   type Wire_Id_Record is record
      --  Kind of wire: signal, variable...
      --  Set at initialization and cannot be changed.
      --  Used to know what is the current value of the wire (could be either
      --  Gate when it is a signal or Cur_Assign when it is a variable).
      Kind : Wire_Kind;

      --  Used in various algorithms: a flag on a wire.  This flag must be
      --  cleared after usage.
      Mark_Flag : Boolean;

      --  Source node that created the wire.
      Decl : Source.Syn_Src;

      --  The initial net for the wire.
      --  This is a pseudo gate that is needed because the value of the wire
      --  can be read before anything was assigned to it.
      Gate : Net;

      --  Current assignment (if there is one).
      --  This is needed so that the current value (for variable) can be read.
      Cur_Assign : Seq_Assign;

      --  Chain of concurrent assigns for this wire.
      --  This is used to detect multiple collision and to handle partial
      --  assignments.
      Final_Assign : Conc_Assign;
      Nbr_Final_Assign : Natural;
   end record;

   type Seq_Assign_Record is record
      --  Target of the assignment.
      Id : Wire_Id;

      --  Assignment in the previous phi context.
      --  Used to restore Cur_Assign of the wire when the phi context is poped.
      Prev : Seq_Assign;

      --  Corresponding phi context for this wire.
      Phi : Phi_Id;

      --  Next wire in the phi context.
      Chain : Seq_Assign;

      --  Value assigned.
      Value : Net;
   end record;

   type Conc_Assign_Record is record
      Next : Conc_Assign;

      --  Concurrent assignment at OFFSET.  The width is set by value width.
      Value : Net;
      Offset : Uns32;

      --  Source of the assignment.  Useful to report errors.
      Stmt : Source.Syn_Src;
   end record;

   type Phi_Type is record
      --  Chain of sequential assignments in the current phi context (BB).
      First : Seq_Assign;
      --  Number of assignments.
      Nbr : Uns32;
   end record;

   package Phis_Table is new Tables
     (Table_Component_Type => Phi_Type,
      Table_Index_Type => Phi_Id,
      Table_Low_Bound => No_Phi_Id,
      Table_Initial => 16);

   package Wire_Id_Table is new Tables
     (Table_Component_Type => Wire_Id_Record,
      Table_Index_Type => Wire_Id,
      Table_Low_Bound => No_Wire_Id,
      Table_Initial => 1024);

   package Assign_Table is new Tables
     (Table_Component_Type => Seq_Assign_Record,
      Table_Index_Type => Seq_Assign,
      Table_Low_Bound => No_Seq_Assign,
      Table_Initial => 1024);

   package Conc_Assign_Table is new Tables
     (Table_Component_Type => Conc_Assign_Record,
      Table_Index_Type => Conc_Assign,
      Table_Low_Bound => No_Conc_Assign,
      Table_Initial => 1024);
end Synth.Environment;